Above An embedded figure drawing from a 1907 issue of The Strand Magazine. Compare that with this observation by Gestalt psychologist Wolfgang Köhler, from his Gestalt Psychology (NY: Liveright, 1947), pp. 92-93—
…sometimes we see from a distance a strange object which later, when we approach it, splits into a well-known thing and parts of other objects… The puzzle-pictures which years ago amused the readers of magazines were examples of this kind of thing. In modern wars it has become a real art to make objects such as guns, cars, boats, etc., disappear by painting upon these things irregular designs, the parts of which are likely to form units with parts of their environment.
Or this from Annie Dillard, Pilgrim at Tinker Creek (NY: Bantam 1975), p. 18—
Nature is like one of those line drawings of a tree that are puzzles for children. Can you find hidden in the leaves a duck, a house, a boy, a bucket, a zebra, and a boot?
This drawing shown here is reminiscent of a double-image painting by Salvador Dali (two nuns who suggest the shape of Robert Houdin's bust of Voltaire), who remembered his interest in puzzles in his article titled "Total Camouflage for Total War" in Esquire Vol 18 No 2 (August 1942), pp. 64-66, 129-130—
Every Saturday [as a child] I received a juvenile publication to which my father had subscribed for me. Its final page was always devoted to a puzzle picture. This would present, for instance, a forest and a hunter. In the tangled underbrush of the forest the artist had cleverly concealed a rabbit; the problem was to find it. Or, again, a doll must be discovered, lost by a child in an apparently empty room. My father would bring me the puzzle, and what was his astonishment to see me find, not one but two, three or four rabbits, not a single doll but several—and never the one which the artist had meant to conceal.